A GUIDE TO WATERING BONSAI

Summer Reading!

"Upon finding that I work as a
professional bonsai artist, many people will remark that they once had a bonsai, but it died and with some regret, they gave up".

Based on the Bonsai Basics section of the hugely successful Bonsai4me.com website and an e-book of the same name, 'Bonsai Basics: The Foundations of Bonsai', written and developed over the past 15 years is out now!

Bonsai,
as with nearly all other types of cultivated plant, require moisture
at their roots to survive. Without a continual source of moisture,
the tree is unable to continue its life process, initially losing
leaves, then branches and finally the entire tree can die. Never doubt that the quickest way of killing a bonsai is to
allow the compost to dry out completely.

However, though the effects of under-watering are immediate, over-watering
a bonsai also causes ill-health in trees. The effects of continual
over-watering takes much longer to become noticeable and can often
be difficult to diagnose.
Established plants and trees growing in the ground have the ability
to 'adjust' to their habitat and the quantity of water that is
available to them. If there is not enough water available to the
root system, the roots will spread out into the soil until enough
moisture can be reliably acquired. Thus plants growing in relatively
dry areas will have far-reaching root systems that will continue
to spread out until a reliable source of moisture can be found.
On the other hand, trees growing in damp conditions where moisture
is permanently available in the upper levels of the soil, will
tend to have shallow root systems as they have easy access to
moisture.

In the confines of a pot, a bonsai loses this ability to self-regulate
its exposure to moisture. It is unable to govern how much or how
little water it accesses. The compost in a bonsai pot is also
far less stable than soil in the ground, its ability to dry out
is greatly increased and it is greatly affected by the outside
influences such as the weather and the surrounding ambient temperature.
Correctly watering your bonsai is a skill itself and is not as
straightforward as one might expect when first starting out. It
is often said in Japan that it takes 3 years to learn to water
correctly. It can sometimes take three years of tree losses before
a bonsai enthusiast realises that it is his/her watering regime
that might be the cause!
THE EFFECTS OF UNDERWATERING AND OVERWATERING

Plants rely on a continual flow of water to stay alive and to
grow. Water is absorbed from the compost into the roots by a process
known as osmosis, the water is then pulled up the body of the
plant and is released into the atmosphere through the foliage.
This process allows the plant to distribute vital nutrients throughout
its structure. However, without a source of moisture at its roots,
this flow of water is interrupted and the plant structure quickly
collapses and dries out. Leaves and branch tips are the first
areas to be affected, followed by branches. Finally the trunk
and roots themselves collapse and dry-out by which time it is
unlikely that the tree will survive without damage. Application
of water at this point is often too late; moisture can actually
be absorbed out of the roots back into the wet compost in a process
known as reverse osmosis.

As previously mentioned, the effects of over-watering a far more
subtle and can take a relatively long period of time to detect.
Over-watering creates an environment for the root system that
is permanently wet. Roots need oxygen to 'breathe' and the presence
of too much water reduces the ability of the compost to absorb
air. This in turn causes the fine root hairs to suffocate and
die. The immediate effect to the tree is a loss of vigour as parts
of its root system are unable to grow and/or dieback.

More worryingly, the dead roots start to rot. Naturally occurring
bacteria are able to colonize the dead tissue and in very wet
composts are able to thrive. As the root system continues to die
back from the effects of overwatering, the root-rotting bacteria
are able to spread throughout the root system and slow (if not
completely stop) the ability of the tree to seal the remaining
live root-tips. Gradually the live portion of the root system
becomes smaller and as it does it is able to support less of the
visible top growth of the tree.

Foliage on the tree will start to yellow and drop; smaller branches
will shrivel and die back. As the live portion of the root-ball
becomes even smaller, it is eventually unable to support the primary
branches and the trunk, causing the tree to die.
Root-rot is often only detected at repotting time in Spring. Rotted
roots will be found to be black and will disintegrate when touched.
The only reliable way of stopping root-rot is to cut away all
dead areas of root.

Bonsai being watered automatically in the garden of Harry Harrington

HOW OFTEN SHOULD I WATER?
As has already been discussed, it is important to avoid the effects
of under-watering and overwatering. So how do you water a bonsai
correctly?

Firstly, NEVER water to a routine. Simply watering on a daily
basis without first observing the condition of the bonsai soil
is often carried out by beginners following the advice of well-meaning
bonsai retailers. Bonsai can indeed require water on a daily or
even twice daily basis, particularly in hot weather or early Spring.
However, watering to a routine commonly leads to permanently wet
compost at other times. If the compost does not lose some of its
moisture content between each watering, it means it is permanently
wet, leading to problems associated with overwatering.

Instead, trees should be checked routinely (at least on
a daily basis), so their water requirements can be observed and
they can then be watered when they actually require it. The surface
of nearly all bonsai composts change colour and appearance when
it starts to dry out. With careful observation, it is always possible
to tell whether or not the compost surface is dry or not. This
can take anything from 12 hours to a week or longer after watering,
depending on a variety of factors such as the surrounding ambient
temperature, plant vigour, pot size and whether it has rained
or not. In the UK, trees tend to need watering daily during the
Summer but with lower temperatures and increased rainfall during
Autumn, Winter and early Spring, watering needs can change day
by day. Never assume that because it has rained your tree has
received enough water particularly during the Summer. Often, it
only rains enough to wet the upper layers of the compost.

The correct time to water is when the top centimetre of the compost
has started to dry out. With regular observation of your trees
on a daily basis, you should be able to apply water when it is
actually required. Allowing the compost to dry a little between
each watering will ensure that they are not overwatered.

Different trees have different water requirements, try to water
individual trees in a collection as they require it, rather than
en masse.